Acoustic respiratory and non-respiratory motion detecting

ABSTRACT

A method of detecting subject respiratory motion and non-respiratory motion includes: transmitting a transmitted signal toward a subject, the transmitted signal being an ultrasound wave, the transmitted signal reflecting off the subject to produce a reflected signal; receiving the reflected signal and converting a form of the reflected signal from ultrasound wave to electrical; comparing the reflected signal to at least a first reference signal to determine at least a first reference phase signal indicative of a first phase difference between the first reference signal and the reflected signal, the at least a first reference signal being associated with the transmitted signal; and analyzing the first reference phase signal for respiratory motion of the subject and non-respiratory motion, the non-respiratory motion including at least one of non-respiratory motion of the subject or motion of an entity other than the subject.

BACKGROUND

Detecting respiration of a patient is desirable, for example to detectabnormal respiration indicating that the patient is in need ofattention. There are many existing techniques to detect respiration,such as impedance plethysmography (the standard for hospitalmonitoring), strain gauges around the patient's chest and/or abdomen,magnetometers, a Respitrace Impedance Plethysmograph (a band around thechest and abdomen), pressure-sensing mattresses, mattresses that sensemovement through capacitive sensors, and direct measures of airway flow,either with a mask or through attachment to an artificial airway of apatient. All of these techniques employ physical contact of one or moreapparatus with the patient.

Several techniques exist to monitor vital signs of a patient withoutdirect physical contact with the patient. For example, microwave radarmay be used with antennas disposed above a prone patient, e.g., attachedto a ceiling above a bed on which the patient lies. Other examplesinclude thermal infrared (with the patient's face being uncovered andkept in view of a thermal-sensing camera), and direct video inspection(with the patient being uncovered or covered but with markings placed onthe patient). Laser interferometry may also be used to monitor patientrespiration if radio interference, interference with materials coveringthe patient, and laser aiming issues are addressed.

SUMMARY

An example of a method of detecting subject respiratory motion andnon-respiratory motion includes: transmitting a transmitted signaltoward a subject, the transmitted signal being an ultrasound wave, thetransmitted signal reflecting off the subject to produce a reflectedsignal; receiving the reflected signal and converting a form of thereflected signal from ultrasound wave to electrical; comparing thereflected signal to at least a first reference signal to determine atleast a first reference phase signal indicative of a first phasedifference between the first reference signal and the reflected signal,the at least a first reference signal being associated with thetransmitted signal; and analyzing the first reference phase signal forrespiratory motion of the subject and non-respiratory motion, thenon-respiratory motion including at least one of non-respiratory motionof the subject or motion of an entity other than the subject.

Implementations of such a method may include one or more of thefollowing features. The analyzing the first reference phase signal fornon-respiratory motion comprises: analyzing a combination of a firstportion of the first reference phase signal and a second portion of thefirst reference phase signal for the non-respiratory motion, the firstportion of the first reference phase signal being within a firstfrequency range, the second portion of the first reference phase signalbeing within a second frequency range, and the second frequency rangebeing separated from the first frequency range. The analyzing thecombination comprises determining a dimensionless magnitude associatedwith the combination. The method further includes: determining thatnon-respiratory motion of the subject is occurring in response to thedimensionless magnitude being above a first threshold and below a secondthreshold; and determining that motion of the entity is occurring inresponse to the dimensionless magnitude being above the secondthreshold. Determining the dimensionless magnitude comprises dividing apower value of the second portion of the first reference phase signal bya power value of the first portion of the first reference phase signal.The first portion of the first reference phase signal is within afrequency range between 0 Hz and 5 Hz, and the second portion of thefirst reference phase signal is within a frequency range between 22 Hzand 50 Hz.

Also or alternatively, implementations of the method may include one ormore of the following features. The first reference signal and thetransmitted signal are both derived from a common electrical drivesignal, the comparing comprises comparing the reflected signal to asecond reference signal, the second reference signal being aphase-shifted version of the first reference signal, to determine asecond reference phase signal indicative of a second phase differencebetween the second reference signal and the reflected signal, theanalyzing the first reference phase signal yields first indicia ofrespiratory motion of the subject, and the method further includes:analyzing the second reference phase signal for second indicia ofrespiratory motion of the subject; and forming composite indicia ofrespiratory motion of the subject comprising the first indicia ofrespiratory motion of the subject when the first reference phase signalis reliable, and comprising the second indicia of respiratory motion ofthe subject otherwise. The transmitting comprises transmitting acontinuous wave ultrasound signal, having a fixed frequency between 30KHz and 100 KHz, as the transmitted signal. The analyzing the firstreference phase signal for non-respiratory motion comprises comparing apower level in a non-respiratory frequency range portion of the firstreference phase signal with a threshold power level.

An example of a motion-detection system includes: a driver configured toproduce a drive signal and to produce a transmitter signal from thedrive signal and a first reference signal from the drive signal; anultrasound transmitter communicatively coupled to the driver andconfigured to transmit a transmitted signal toward a subject in responseto the transmitter signal, the transmitted signal being an ultrasoundwave; a receiver configured to receive a reflected signal and convert aform of the reflected signal from ultrasound wave to electrical; a phasedifference device, communicatively coupled to the driver and thereceiver, configured to compare the reflected signal to at least thefirst reference signal to determine at least a first reference phasesignal indicative of a first phase difference between the firstreference signal and the reflected signal, the at least a firstreference signal being associated with the drive signal; and a signalanalyzer communicatively coupled to the phase difference device andconfigured to analyze the first reference phase signal to determinerespiratory motion of the subject and non-respiratory motion, thenon-respiratory motion including at least one of non-respiratory motionof the subject or motion of an entity other than the subject.

Implementations of such a system may include one or more of thefollowing features. The signal analyzer comprises non-respiratory motionmodule configured to analyze a combination of a first frequency portionof the first reference phase signal and a second frequency portion ofthe first reference phase signal for the non-respiratory motion, thefirst frequency portion of the first reference phase signal being withina first frequency range, the second frequency portion of the firstreference phase signal being within a second frequency range, and thesecond frequency range being separated from the first frequency range.The non-respiratory motion module is configured to: determine adimensionless magnitude associated with a combination of the firstfrequency portion of the first reference signal and the second frequencyportion of the first reference phase signal; provide an indication thatnon-respiratory motion of the subject is occurring if the dimensionlessmagnitude is above a first threshold and below a second threshold; andprovide an indication that motion of the entity is occurring if thedimensionless magnitude is above the second threshold. Thenon-respiratory motion module is configured to determine thedimensionless magnitude by dividing a power value of the secondfrequency portion of the first reference phase signal by a power valueof the first frequency portion of the first reference phase signal. Thefirst frequency portion of the first reference phase signal is within afrequency range between 0 Hz and 5 Hz, and the second frequency portionof the first reference phase signal is within a frequency range between22 Hz and 50 Hz.

Also or alternatively, implementations of the system may include one ormore of the following features. The the driver is further configured toproduce a second reference signal from the drive signal, the secondreference signal being a phase-shifted version of the first referencesignal, the phase difference device comprises: a first comparatorconfigured to compare the reflected signal to the first reference signalto determine the first reference phase signal and a second comparatorconfigured to compare the reflected signal to the second referencesignal to determine a second reference phase signal indicative of asecond phase difference between the second reference signal and thereflected signal, and the signal analyzer is configured to form acomposite subject respiratory signal by combining a firstphase-differential portion of the first reference phase signal with asecond phase-differential portion of the second reference phase signal,the first phase-differential portion of the first reference phase signalbeing within a desirable output range of the first comparator and thesecond phase-differential portion of the second reference phase signalcorresponding to times when the first phase-differential portion of thefirst reference phase signal is outside the desirable output range ofthe first comparator. The driver is configured to produce thetransmitter signal with a frequency between 35 KHz and 45 KHz. Thesignal analyzer comprises non-respiratory motion module configured tocompare a power level in a non-respiratory frequency range portion ofthe first reference phase signal with a threshold power level.

Items and/or techniques described herein may provide one or more of thefollowing capabilities, as well as other capabilities not mentioned.Patient respiration, non-respiratory motion of a patient, and motion ofan entity other than the patient may be identified and differentiated,and may be done so by a single device in a non-invasive manner. Patientrespiration information may be used to implement a synchronizer formechanical ventilation that may be independent of a mechanicalventilator. Synchronization may be provided between an aerosol generatorand a patient's breathing effort, e.g., for more effective delivery of avariety of drugs administered by inhalation including, but not limitedto, bronchodilators, antibiotics, chemotherapy agents, and replacementlung surfactants. Pulmonary functions measurements may be aided, e.g.,for determination of respiratory system resistance (or conductance),and/or resonant frequency of a respiratory system based on the forcedoscillation method. An x-ray machine may be triggered at the end ofinspiration. Respiratory rate and/or respiratory effort may bedetermined. Caretaker movement may be assessed, e.g., for documentingcare being given a patient, for charting patient acuity and/or billing,for assessing physiological effects of patient handling, and/or workstudies of nursing care and other actioners. Sleep polysomnography maybe implemented or aided. Patient overall well-being assessment can beimplemented or aided. Patient agitation can be detected and/or assessed.Neurological disorders such as seizures, effects of anti-convulsingtherapies, and/or tremulousness can be detected and/or assessed. Drugwithdrawal, especially in infants, can be detected and/or assessed.Patient presence, e.g., for elder care, can be detected. Patient comfortand overall well-being can be assessed. Sleep apnea and infant apnea canbe detected, and differential diagnosis of obstructive apnea performed.Movement of humans or animals during recovery from anesthesia can beassessed. Movement of animals in laboratory experiments of drugs can bedetermined. Systemic infections in infants and others may be detectedearly, e.g., based on decreased movement. Recovery of a respiratorysignal after a high-frequency movement is rapid. High resolution, e.g.,less than 100 ms, of very short movements typically of non-respiratorymovements in infants may be provided. Unambiguous detection ofrespiratory movement within and across displacements of multiplewavelengths may be provided. Other capabilities may be provided and notevery implementation according to the disclosure must provide any, letalone all, of the capabilities discussed. Further, it may be possiblefor an effect noted above to be achieved by means other than that noted,and a noted item/technique may not necessarily yield the noted effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a system for determiningrespiratory motion of a patient, non-respiratory motion of the patient,or motion of another entity.

FIG. 2 is a block diagram of an example implementation of the systemshown in FIG. 1.

FIG. 3 is a phase versus voltage characteristic of examples of averagedphase signals produced by comparators shown in FIG. 2.

FIG. 4 is a timing diagram of output signals of a phase differencedevice shown in FIG. 1 corresponding to motion of the patient shown inFIG. 1.

FIG. 5 is a block diagram of components of a signal analyzer shown inFIG. 1.

FIG. 6 is a functional block diagram of the signal analyzer shown inFIG. 5.

FIG. 7 is a block flow diagram of an example algorithm implemented bythe signal analyzer shown in FIG. 6.

FIG. 8 is a block flow diagram of a process of detecting respiratory andnon-respiratory motion.

FIG. 9 is a block diagram of an analog implementation of the signalanalyzer shown in FIG. 6.

FIG. 10 is a composite diagram of experimental data derived from use ofan example implementation of the system shown in FIG. 1.

DETAILED DESCRIPTION

Techniques are discussed herein for detecting motion, and in particulardetecting respiratory motion of a patient and other motion. For example,in addition to respiratory motion of a patient, non-respiratory motion,including non-respiratory motion of the patient and/or motion of anotherentity (not the patient), may be detected. The non-respiratory motionmay be differentiated and identified. In an example technique to detectmotion, a phase difference signal between an ultrasound signal reflectedoff the patient and a reference signal is determined. Magnitude changesin the phase difference signal are analyzed to determine patientrespiratory motion, both the amount of motion and the direction (towardor away from a sensor detecting the reflected signal). Further, a ratioof magnitudes of different frequency portions of the phase differencesignal is analyzed to determine the existence of motion other thanpatient respiratory motion, and to classify any such existing motion.These examples, however, are not exhaustive.

Referring to FIG. 1, a system 10 includes a driver 12, a transmitter 14,a receiver 16, a phase difference device 18, and a signal analyzer 20.The system 10 is an example of a system configured to detect andidentify respiratory motion of a subject or patient 22, non-respiratorymotion of the patient 22, and motion of a non-patient entity (e.g., aperson 24, a piece of equipment, etc.). The person 24 could be, forexample, a caretaker. Although referred to herein throughout as thepatient 22, the subject being monitored need not be a patient, and canbe a human or an animal. Also, the patient 22, as used herein, includesboth the person of the patient 22 and any coverings on the personincluding clothing (e.g., a hospital Johnny), a bed sheet, a blanket,etc. The system 10 is an ultrasound system configured to determinemotion non-invasively. The system 10 is non-invasive in that the patient22 need not be contacted by any equipment or have any equipment insertedinto the patient 22, even though sound waves may penetrate the patient22. The transmitter 14 preferably makes no physical or electricalcontact with the patient 22. The transmitter 14 and the receiver 16combined may be referred to as a sensor 15. The system 10 is an exampleof an acoustic respiratory movement sensor (ARMS).

As an example, the system 10 may be used to produce a continuousultrasound signal and use reflections of the signal from the patient 22to determine movement of the patient or one or more other entities. Forexample, the driver 12 may cause the transmitter 14 to produce acontinuous ultrasound signal with a frequency between 35 KHz and 45 KHz,preferably about 40 KHz (above the range of human hearing), with thetransmitter 14 directed and configured to produce a conical-shapedradiation pattern that covers a torso of the patient 22 in response to adrive signal from the driver 12. The ultrasound signal transmitted bythe transmitter 14 will reflect off the patient 22 and the reflectedsignal may be received by the receiver 16 that is directed andconfigured to receive ultrasound signals reflected off the patient 22from the transmitter 14. Movement of the patient 22 will cause thereflected signal to have a slight shift in its phase with respect to thetransmitted signal due to the Doppler effect. This phase shift will bedetected, and an indication of the phase difference over time provided,by the phase difference device 18. The indication of the phasedifference will be processed by the signal analyzer 20 to provide one ormore indications of respiratory movement of the patient 22(corresponding to changes in the phase difference indicated by the phasedifference device 18), and/or one or more indications of non-respiratorymovement. The non-respiratory movement may include movement of thepatient 22 that is not of respiratory origin and/or movement of anotherentity (i.e., non-patient movement) such as a caretaker of the patient,equipment near the patient 22, etc. An example implementation of thesystem 10, other than the signal analyzer 20, is shown in FIG. 2, whichis discussed in more detail below with respect to the discussion of thecomponents of FIG. 1.

The driver 12 is communicatively coupled to the transmitter 14 andconfigured to produce an electrical drive signal to induce thetransmitter 14 to produce an acoustic ultrasound signal. For example,referring also to FIG. 2, the driver 12 includes a crystal oscillator32, a drive module 34, and a variable gain power amplifier 36. Theoscillator 32 is communicatively coupled to the drive module 34, whichis communicatively coupled to the power amplifier 36, which iscommunicatively coupled to the transmitter 14. The drive module 34includes, in this example, a dual by-quinary divider that includes adivide-by-25 circuit 38 communicatively coupled to the oscillator 32,and a divide-by-four circuit 40 communicatively coupled to thedivide-by-25 circuit 38 and the power amplifier 36. An output of thedivide-by-25 circuit 38 is communicatively coupled to the phasedifference device 18 that is discussed further below. The oscillator 32is configured to produce a 4 MHz square wave. The divide-by-25 circuit38 is configured to divide the signal output by the oscillator 32 by 25to produce a 160 kHz square wave. The divide-by-four circuit 40 isconfigured to divide the output signal of the divide-by-25 circuit 38 byfour, in this case to produce a 40 kHz square wave that is provided tothe variable gain power amplifier 36. The variable gain power amplifier36 is configured to amplify the signal output by the divide-by-fourcircuit 40 to produce an amplified signal as a drive output signal 37 ofthe driver 12.

The drive output signal 37 of the driver 12 is provided to thetransmitter 14 by the amplifier 36. The transmitter 14 comprises atransducer configured to convert the electrical signal provided by thepower amplifier 36 into an acoustic signal. For example, the transmitter14 may comprise a piezoelectric transducer. The transmitter 14 isdirected toward the patient 22 such that the acoustic signal will bedirected to and reflect off of the patient 22.

The receiver 16 comprises a transducer configured to convert thereflected acoustic signal into an electric signal. For example, thereceiver 16 may comprise a piezoelectric transducer similar to thetransmitter 14. The receiver 16 may comprise more than one transducer,for example, a collection of uncoordinated transducers, an array, suchas a phased-array, of transducers, and/or a combination of these, thatmay provide greater spatial definition of the patient 22 and/or otherentity than a single transducer could. The transduced reflected signalis provided as an output of the receiver 16 to the phase differencedevice 18 as an input.

The phase difference device 18 is configured to determine and provide anindication of a phase difference between a reference signal from thedriver 12 and the electrical form of the reflected signal provided bythe receiver 16. The reference signal from the driver 12 may be theactual electrical drive output signal 37 provided to the transmitter 14or another signal related to the drive output signal. For example, inthe implementation of the system 10 shown in FIG. 2, the output signalfrom the divide-by-25 circuit 38 is an intermediate output signal andmay be used as a reference signal 60 provided to the phase differencedevice 18 from the driver 12. The reference signal 60 is likely to beout of phase with the drive reference signal 37, but the phaserelationship between the signals 37, 60 will be constant. The phaserelationship between the reference signal 60 and the reflected signalwill change as the patient 22 moves due to the Doppler effect. Thischange in the phase relationship may be determined and used by thesignal analyzer 20 to determine an indication of respiratory motion ofthe patient 22. Further, the power in a phase relationship signal,corresponding to the phase relationship between the reference signal 60and the reflected signal, can be used by the signal analyzer todetermine one or more indications of non-respiratory motion either ofthe patient 22 or another entity.

Further in the example of FIG. 2, the phase difference device 18includes a variable gain amplifier/filter 42, a comparator 44, acomparison module 46, and a smoothing module 48. The receiver 16 iscoupled to the variable gain amplifier/filter 42, which is coupled tothe comparator 44, which is coupled to the comparison module 46, whichis coupled to the smoothing module 48. The variable gainamplifier/filter 42 is configured to receive the output signal from thereceiver 16, that is, the reflected signal in electrical form, toamplify the signal several thousand times, and to filter unwantedsignals, e.g., noise produced by other portions of the system 10. Thevariable gain amplifier/filter 42 is configured to provide the amplifiedand filtered reflected signal to the comparator 44, which is configuredto convert the reflected signal into a reflected signal 45 that is asquare wave at logic levels zero and one. The comparator 44 is coupledand configured to provide the reflected signal 45 to the comparisonmodule 46 to determine a phase difference between the reflected signal45 and the reference signal 60 provided by the driver 12. The reflectedsignal as used herein includes not only the ultrasound energy reflectedoff the patient 22, but the various forms of the electrical signalproduced in response to the reflected ultrasound, e.g., by the receiver16, the amplifier/filter 42, and the comparator 44.

In the example implementation of the system 10 shown in FIG. 2, thecomparison module 46 includes a dual D-flip-flop 52, a Phase Acomparator 54, and a Phase B comparator 56. Other configurations may beused for the comparison module 46, including a single phase comparatorbeing used such as the comparator 54. The flip-flop 52 is coupled to thedrive module 34 to receive the reference signal and to convert thereference signal 60 into a Phase A clock signal 62 and a Phase B clocksignal 64, each with a frequency of the drive output signal 37, here 40KHz. The signals 62, 64 are square waves that are out of phase withrespect to each other. For example, the signal 62 may be 90° out ofphase with the signal 64, with the signal 64 lagging the signal 62,although other phase differences and relationships (leading/lagging) maybe used. The example of the signal 62 being 90° out of phase with thesignal 64 (i.e., in phase and quadrature phase) is used based upon theparticular performance characteristics of the comparators 54, 56. Here,the comparators 54, 56 may be model CD4046 comparators made by TexasInstruments® Incorporated of Dallas, Tex., USA that have substantiallylinear behavior with respect to phase differences of input signals thatproduce an output signal between 0.5V and 4.5V. For this examplecomparator, these output signal voltages correspond to phase differencesbetween about 36 degrees and about 144°, and between about 216° andabout 324° (as discussed more fully further below with respect to FIG.3). Thus, a phase difference of 90° will ensure that a phase differencedetermined by at least one of the comparators 54, 56 will always be inthe linear range of the respective comparator(s) 54, 56. The outputsignal voltage range of 0.5V to 4.5V is thus a desired operational rangeof the comparators 54, 56 and may be considered the linear range of thecomparators 54, 56. The linear range may be artificially selected with amargin of safety such that the upper and lower thresholds specified forthe linear range of the comparators 54, 56 (here, 4.5V and 0.5V of theoutput signals of the comparators 54, 56) may not be the extremes of thelinear capability of the comparators 54, 56, but selected to help reducenoise sensitivity and help ensure or improve accuracy of determinedrespiratory motion. Thus, even though the comparators 54, 56 may performlinearly for at least some range outside of the designated linear range,the comparators 54, 56 may be considered to be outside their linearranges if either threshold is exceeded (i.e., the output signal voltagebeing below the lower threshold or above the upper threshold). Usingonly outputs of the comparators 54, 56 that are within the linear rangehelps improve the accuracy of the determined phase relationship betweenthe reflected signal 45 and the reference signal 60 by avoidinghigh-sensitivity portions of the ranges of the comparators 54, 56 whichreduces noise sensitivity of the comparators 54, 56.

The comparators 54, 56 are configured to use the reflected signal 45provided by the comparator 44 as one input and a respective one of thesignals 62, 64 as the other input. Thus, the Phase A comparator 54 usesas inputs the reflected signal 45 (shown as input S) and the Phase Aclock signal 62 (shown as a phase comparator input (PCI)), and the PhaseB comparator 56 uses as inputs the reflected signal 45 (shown as aninput S) from the comparator 44 and the Phase B clock signal 64 (shownas a phase comparator input (PCI)). The Phase A comparator 54 isconfigured to determine the phase difference between the reflectedsignal 45 and the Phase A clock signal 62 and the Phase B comparator 56is configured to determine the phase difference between the reflectedsignal 45 and the Phase B clock signal 64. The Phase A comparator 54 isconfigured to provide the phase difference between the reference signal45 and the Phase A clock signal 62 as an output signal 74 (shown asphase comparator output (PCO)). The Phase B comparator 56 is configuredto provide the phase difference between the reference signal 45 and thePhase B clock signal 64 as an output signal 76 (shown as phasecomparator output (PCO)). The comparison module 46 is configured andcoupled to the smoothing module 48 to provide the output signals 74, 76to the smoothing module 48.

The smoothing module 48 is configured to provide a smooth signalindicating the phase difference between the reflected signal 45 and thereference signal 60. In the example shown in FIG. 2, the smoothingmodule 48 is configured to provide smoothed signals that indicate thephase difference between the reflected signal 45 and the Phase A and Bsignals 92, 96. The smoothing module 48 in this example includes a PhaseA low-pass filter (LPF) 82, a Phase A flip-flop 84, a Phase B LPF 86,and a Phase B flip-flop 88. More or fewer filters and flip-flops may beused, for example if only a single comparator is used in the comparisonmodule 46. The Phase A LPF 82 is coupled to the Phase A comparator 54and configured to smooth, e.g., average, the output signal 74 from thePhase A comparator 54 to produce a Phase A signal 92. The Phase B LPF 86is coupled to the Phase B comparator 56 and configured to smooth, e.g.,average, the output signal 76 from the Phase B comparator 56 to producea Phase B signal 96. The Phase A LPF 82 and the Phase B LPF 86 are eachpreferably a resistor-capacitor network with a time constant of 0.1 msin the example of a 40 kHz drive output signal 37, although otherconfigurations with other time constants, including longer or shortertime constants, may be used. The flip-flops 84, 88 are D flip-flops thatare coupled to receive the Phase A output signal 74 and the Phase Bcomparator output signal 76, respectively, at respective data inputs andto receive the Phase A clock signal 62 and the Phase B clock signal 64,respectively, at respective clock signal inputs. The flip-flops 84, 88will thus produce, respectively, a polarity bit A signal 94 and apolarity bit B signal 98 indicative of a phase quadrant in which therespective phase signal is, and that can be used to ensure the correctpolarity of a respiratory movement signal as discussed further below.

As discussed above, the Phase A clock signal 62 and the Phase B clocksignal 64 are out of phase with respect to each other. Because the PhaseA comparator 54 and the Phase B comparator 56 both compare these signalsrespectively to the same signal, i.e., the reflected signal 45, thePhase A signal 92 and the Phase B signal 96 will be out of phase withrespect to each other by the same amount as the clock signals 62, 64.

Referring also to FIG. 3, in a phase space 100 the Phase A signal 92(shown as ϕ_(A)) is 90° out of phase with the Phase B signal 96 (shownas ϕ_(B)), with the signal 96 (ϕ_(B)) lagging or leading the signal 92(ϕ_(A)) depending upon whether motion of the patient 22 is toward oraway from the receiver 16. FIG. 3 is a phase-space diagram of phasedifference with respect to the reflected signal 45, with phases being anangle about a center point 120, and a vertical position on a phasecircle 122 corresponding to a voltage value of a corresponding phasesignal, here the Phase A signal 92 or the Phase B signal 96. The bottomof a vertical axis has been chosen to be 0°, or no relative phasedifference between the transmitted and received signals, with a top ofthe vertical axis 124 therefore being 180° of phase difference.Consequently, a right-hand side of a horizontal axis 126 corresponds to90° of phase difference and a left-hand side of the horizontal axis 126corresponds to 270° of phase difference. The Phase A signal 92 is shownas a Phase A vector 102 and the Phase B signal 96 is shown as a Phase Bvector 104.

As the patient 22 moves toward the sensor 15, the phase of the reflectedsignal leads that of the transmitted signal, since the time to return isdecreased. As the patient 22 moves away from the sensor 15, the phase ofthe reflected signal lags that of the transmitted signal, since the timeto return is increased. As the patient 22 moves toward the sensor 55,the vectors 102, 104 are both moving counter-clockwise in the phasespace. Both the Phase A and Phase B signals 92, 96 are increasing whenboth vectors 102, 104 are in quadrant 1 (QI) and quadrant 2 (QII) of thephase space 100, and are decreasing when both the vectors 102, 104 arein quadrant 3 (QIII) and quadrant 4 (QIV) with continuedcounter-clockwise rotation. The polarity bit A and B signals 94, 98 areset by the flip-flops 84, 88 that detect whether the trailing edge ofthe reflected signal leads the trailing edge of the transmitted signal,as in QI and QII, or lags the trailing edge of the transmitted signal,as in QIII and QIV, being set to 1 in QI and QII, and 0 in QIII and QIV.In this way, the position of the two vectors 102, 104 can beunambiguously determined from the polarity bit A and B signals 94, 98 soas determine the direction of changes in the Phase A signal 92 and thePhase B signal 96.

From FIG. 3, the behavior of the signals 92, 96 can be seen withreference to the vectors 102, 104. If the Phase A vector 102 is in QIII,then the Phase B vector 104 will be in QII. During movement of the PhaseA vector 102 counter-clockwise through QIII (the patient 22 movingtoward the sensor 15), the Phase A signal 92 is decreasing, and thePhase B signal 96 is increasing. When the Phase A vector 102 enters QIV,the Phase B vector 104 enters QIII. With further movement of the patient22 toward the sensor 15 with the Phase A vector entering QI, the Phase Asignal 92 will increase and the Phase B signal 96 will decrease. Whenthe Phase A vector 102 is in QI or QII, when the flip-flop 84 isclocked, the Phase A output signal 74 will be a logical 1 and thus thepolarity bit A signal 94 will be set to a logical 1. The same appliesfor the Phase B polarity bit signal 98. When the Phase A vector 102 isin QIII or QIV, when the flip-flop 84 is clocked, the Phase A outputsignal 74 will be a logical 0 and thus the polarity bit A signal 94 willbe set to a logical 0. The same applies for the Phase B polarity bitsignal 98.

Lines 106, 108 indicate threshold levels, here 0.5V and 4.5V, ofaveraged phase signal levels corresponding to the linear range limits ofthe comparators 54, 56 in the example of the comparators 54, 56 beingmodel CD4046 comparators made by Fairchild Semiconductor Corporation.Below the line 106 or above the line 108, a large phase angle changeresults in a small voltage change, and thus these phase angle ranges arepreferably avoided so that the outputs of the comparators 54, 56 areonly used when the comparators 54, 56 are in their linear ranges toreduce noise. The phase angles at 0.5V corresponding to the line 106 are36° and 324° in QI and QIV, and the phase angles at 4.5V correspondingto the line 108 are 144° and 216° in QII and QIII, respectively. Sincethe Phase A vector 102 and the Phase B vector 104 are fixed at 90° fromeach other, when the Phase A vector 102 (corresponding to the Phase Asignal 92) enters a bottom or top out-of-specification zone, i.e., belowthe line 106 or above the line 108 (with the Phase A signal 92 below0.5V or above 4.5V), the Phase B vector 104 is within an allowed zonebetween the lines 106, 108. The signal analyzer 20, as discussed morefully below, is configured to detect whether the Phase A vector 102 (thePhase A signal 92) is in the allowed zone, and if not, to select thePhase B signal 96 for computations of respiratory motion. The range of0.5V to 4.5V is an example only and other ranges may be used, either forthe example comparators 54, 56 and/or other comparators. With the rangeof 0.5V to 4.5V chosen, and with the Phase A signal 92 used as thedefault signal, the Phase A signal 92 will be predominantly used forcomputations for respiratory motion.

Referring also to FIG. 4, a timing diagram 200 shows relative timing ofthe Phase A signal 92, the polarity bit A signal 94, the Phase B signal96, the polarity bit B signal 98 corresponding to motion of the patient22 relative to the sensor 15, and an indication of which of the phasesignals 92, 96 is used at any given time. In FIG. 4, the patient 22moves toward the sensor 15 for about 2.5 wavelengths, then reverses andmoves away from the sensor 15 for just under one wavelength. This is theequivalent of counter-clockwise movement of the phase vectorapproximately 900 degrees, and then clockwise movement of approximately300 degrees. At a time t₀, the Phase A signal 92 increases from 0Vtoward 5V as the patient 22 moves toward the sensor 15. At a time t₁,the Phase A signal 92 reaches 5 V, and reverses direction, returningfrom 5V at the time t₁ to 0V at a time t₂. This pattern continues untilthat time t₃ when the patient 22 stops moving toward the center 15 andreverses direction, moving away from the sensor 15 from the time t₃until a time t₄. From the time t₀ until the time t₃, with the patient 22moving toward the sensor 15, the Phase B signal 96 lags the Phase Asignal 92 (i.e., the Phase A signal 92 leads the Phase B signal 96) by90°. From the time t₃ until the end of the record, with the patient 22moving away from the sensor 15, the Phase B signal 96 leads the Phase Asignal 92 (i.e., the Phase A signal 92 lags the Phase B signal 96) by90°. While the patient 22 is moving toward the sensor 15, the polaritybit A signal 94 is a logical 1 during time intervals when voltage of thePhase A signal 92 is increasing and a logical 0 during time intervalswhen the voltage of the Phase A signal 92 is decreasing. The sameapplies for the polarity bit B signal 98 with respect to the Phase Bsignal 96. Conversely, while the patient 22 is moving away from thesensor 15, the polarity bit A signal 94 is a logical 1 during timeintervals when the voltage of the Phase A signal 92 is decreasing and alogical 0 during time intervals when the voltage of the Phase A signal92 is increasing. The phase diagram in FIG. 3 shows the correspondencebetween the polarity bit and the quadrant of the phase vector. The sameapplies for the polarity bit B signal 98 with respect to the Phase Bsignal 96. Out-of-specification conditions are indicated by intervals130 during which the Phase B signal 96 will be used, while during allother times, the Phase A signal 92 will be used for the exampleimplementation being discussed herein.

The phase relationship between the reference signal 60 and the reflectedsignal provided by the phase difference device 18, and in particular thecomparison module 46 and the smoothing module 48, may be used by thesignal analyzer 20 to determine respiratory motion of the patient 22 andnon-respiratory motion either of the patient 22 or another entity. Forexample, the change in the phase relationship can be determined, e.g.,as discussed further below by differentiating one or more phaserelationship signals provided by the phase difference device 18, as anindication of the motion of the patient 22.

Referring to FIG. 5, an example of the signal analyzer 20 comprises acomputer system including a processor 132, a non-transitory memory 134including (optionally) software 136, and a display 138. The processor132 is preferably an intelligent device, e.g., a personal computercentral processing unit (CPU) such as those made or designed byQUALCOMM®, Intel® Corporation, ARM®, or AMD®, a microcontroller, anapplication specific integrated circuit (ASIC), etc. The processor 132could comprise multiple separate physical entities that can bedistributed in the signal analyzer 20. The memory 134 may include randomaccess memory (RAM) and read-only memory (ROM). The memory 134 is aprocessor-readable storage medium that may store the software 136 whichis processor-readable, processor-executable software code containinginstructions that are configured to, when executed, cause the processor132 to perform various functions described herein (although thedescription may refer only to the processor 132 performing thefunctions). Alternatively, the software 126 may not be directlyexecutable by the processor 132 and instead may be configured to causethe processor 132, e.g., when compiled and executed, to perform thefunctions. The software 136 can be loaded onto the memory 134 by beingdownloaded via a network connection, uploaded from a disk, etc. Thedisplay 138 is a liquid-crystal display (LCD) (e.g., a thin-filmtransistor (TFT) display), although other forms of displays areacceptable, e.g., a cathode-ray tube (CRT). The processor 132, thememory 134, and the display are communicatively coupled to each other.

Referring to FIG. 6, with further reference to FIGS. 1 and 5, the signalanalyzer 20 includes a non-respiratory motion module (means fordetermining non-respiratory motion) 140 and a respiratory motion module(means for determining respiratory motion) 142. The non-respiratorymotion module 140 includes a filter module (means for filtering) 152, apower calculating and smoothing module (means for calculating power andsmoothing) 154, a comparison module (means for determining a comparison)156, and a motion type module (means for determining a motion type) 158.The modules 140 (including the modules 152, 154, 156, 158), 142 arefunctional modules implemented by the processor 132 and the software 136stored in the memory 134. Thus, reference to any of the modules 140,142, 152, 154, 156, 158 performing or being configured to perform afunction is shorthand for the processor 132 performing or beingconfigured to perform the function in accordance with the software 136(and/or firmware, and/or hardware of the processor 132). Alternatively,one or more of the modules 142, 152, 154, 156 and 158 could beimplemented using analog circuitry without microprocessor support, orusing a combination of analog circuitry and processor support.Similarly, reference to the processor 132 performing a functiondiscussed with respect to the signal analyzer 20, is equivalent to therespective module(s) 140, 142, 152, 154, 156, 158 performing thefunction.

The non-respiratory motion module 140 is configured to determine if thepatient 22 is moving aside from breathing, i.e., if non-respiratorymotion of the patient 22 is present, and if there is motion present ofan entity other than the patient 22. The module 140 is configured todetermine if either of these types of motion is present, and todistinguish between and provide indications of these types of motion bydetermining and analyzing a normalized magnitude of a frequency range ofthe phase relationship between the reference signal and the reflectedsignal. The phase relationship between the reference signal and thereflected signal is normalized to a frequency range associated withrespiration of the patient 22.

The filter module 152 is configured to separate different frequencyranges of the phase relationship between the reference signal and thereflected signal as indicated by the phase difference device 18.Referring also to, and in an example implementation of an algorithmimplemented by the signal analyzer 20 shown in, FIG. 7, the filtermodule 152 is configured to filter the Phase A signal 92 from the phasedifference device 18 into two frequency bands. In the example shown inFIG. 7, at stages 162, 172 the filter module 152 is configured tolow-pass filter the Phase A signal 92 into a respiration frequency bandand to band-pass filter the Phase A signal 92 into a non-respirationfrequency band. The respiration frequency band is a range of frequenciesthat are likely to include frequencies of respiration of the patient 22.For example, as shown in FIG. 7 at a stage 162, the respirationfrequency band may be from 0 Hz to 5 Hz, which is a band associated withrespiration of an infant. The non-respiration frequency band is a rangeof frequencies that are likely to include frequencies of non-respiratorymotion of entities other than the patient 22. For example, as shown inFIG. 7 at a stage 172, the non-respiration frequency band may be between22 Hz and 50 Hz, and preferably from 28 Hz to 33 Hz as shown. Therespiration frequency band is different from, and preferably separatedfrom the non-respiration frequency band. Preferably, the LPF 162suppresses signals in the non-respiration frequency band by at least 10dB. Also preferably, the BPF 172 suppresses signals in the respirationfrequency band by at least 10 dB.

The power calculating and smoothing module 154 is configured todetermine power contained in the filtered signal portions from thefilter module 152 and smooth the determined values for use in acomparison of the two powers. As shown in stages 164 and 166, the module154 is configured to calculate a power in the respiration-band filteredsignal determined at stage 162, and to smooth (e.g., average) thecalculated power over time to determine a respiration power value.Similarly, as shown in stages 174 and 176, the module 154 is configuredto calculate a power in the non-respiration-filtered signal determinedat stage 172, and to smooth (e.g., average) the calculated power overtime to produce a non-respiration power value.

The comparison module 156 is configured to compare the non-respirationpower value to the respiration power value from the power calculatingand smoothing module 154 to determine motion parameter value. As shownat stage 182 of FIG. 7, the module 156 is configured to calculate acomparison of signal power in the non-respiration frequency band andsignal power in the respiration frequency band, here calculate a ratio,of the non-respiration power value to the respiration power value todetermine the motion parameter value, which is a dimensionless number, adimensionless magnitude of the power ratio.

The motion type module 158 is configured analyze the motion parametervalue from the ratio module 156 to determine which type ofnon-respiratory motion, if any, is present in a region detectable by thesensor 15 (i.e., a field of “view” of the sensor 15). The module 158 canclassify non-respiratory motion into non-respiratory patient motion, ormotion of an entity other than the patient 22 (a non-patient entity,i.e., a non-subject entity). For example, the motion type module 158 canclassify different motions based upon threshold values for the motionparameter value. For example, the module 158 may determine that nonon-respiratory motion is present if the motion parameter value is below0.004, that there is non-respiratory motion of the patient 22 if themotion parameter value is in a range from 0.004 to 0.02, or that thereis non-respiratory motion of an entity other than the patient 22 if themotion parameter value is above 0.02. As shown at stage 184, the module156 is configured to provide an output that indicates the type(s) ofmotion present or the lack of non-respiratory motion being present.Alternatively, the module 156 may be configured to indicate thatnon-respiratory motion is present without indicating which type ofnon-respiratory motion is present.

The respiratory motion module 142 is configured to process theindication, provided by the phase difference device 18, of the phaserelationship between the reflected signal and the reference signal todetermine and provide an indication of respiratory motion of the patient22. In particular, the respiratory motion module 142 is configured todetermine a change in the phase relationship between the reflectedsignal and the reference signal to produce time-varying informationindicative of the patient's respiratory motion. This time-varyinginformation may be in the form of a time-varying voltage that may beplotted to show the patient's respiratory motion. For example, a trace220 shows the time-varying voltage corresponding to an example where thepatient 22 has constant-speed respiratory motion, and a trace 222 showsthe motion in distance as a function of time, here the motion being 2 cmmoving toward the sensor 15 and then about 1 cm moving away from thesensor 15.

FIG. 7 shows stages of an example algorithm of the respiratory motionmodule 142 for the example implementation of the driver 12, thetransmitter 14, the receiver 16, and the phase difference device 18shown in FIG. 2. The respiratory motion module 142 is configured toreceive as inputs, at a stage 190, the Phase A signal 92, the polaritybit A signal 94, the Phase B signal 96, and the polarity bit B signal 98to determine the respiratory motion of the patient 22. In this example,the module 142 is configured to use the Phase A signal 92 while thePhase A comparator 54 is in a linear operation range, here while thePhase A signal 92 is between 0.5V and 4.5V. That is, the module 142 isconfigured to use the Phase A signal 92 unless the Phase A signal 92 isbelow 0.5V or above 4.5V, i.e., unless the Phase A comparator 54 isoutside a linear operation range. Thus, as shown by a stage 192, themodule 142 is configured to determine whether the Phase A signal 92 iswithin a range from 0.5V to 4.5V.

The respiratory motion module 142 is configured to respond to the PhaseA signal 92 being between 0.5V and 4.5V by processing the Phase A signal92 to determine respiratory motion of the patient 22, and being below0.5V or above 4.5V by processing the Phase B signal 94 to determinerespiratory motion of the patient 22. The module 142 is configured torespond to the Phase A signal 92 being between 0.5V and 4.5V bydetermining, at stage 194, whether the polarity bit A signal 94 is alogical 1 or a logical 0. The module 142 is configured to respond to thepolarity bit A signal 94 being a logical 1 by differentiating, at stage196, the Phase A signal 92 to determine the change in the Phase A signal92 which is an indication of the patient's respiratory motion with thepolarity bit A signal 94 being a logical 1. The module 142 is configuredto respond to the polarity bit A signal 94 being a logical 0 bydifferentiating and then inverting, at stage 198, the Phase A signal 92to determine the inverse of the change in the Phase A signal 92 which isan indication of the patient's respiratory motion with the polarity bitA signal 94 being a logical 0. The module 142 is configured to respondto the Phase A signal 92 being below 0.5V or above 4.5V by determining,at stage 200, whether the polarity bit B signal 98 is a logical 1 or alogical 0. The module 142 is configured to respond to the polarity bit Bsignal 98 being a logical 1 by differentiating, at stage 202, the PhaseB signal 96 to determine the change in the Phase B signal 96 which is anindication of the patient's respiratory motion with the polarity bit Bsignal 98 being a logical 1. The module 142 is configured to respond tothe polarity bit B signal 98 being a logical 0 by differentiating andthen inverting, at stage 204, the Phase B signal 96 to determine theinverse of the change in the Phase B signal 96 which is an indication ofthe patient's respiratory motion with the polarity bit B signal 98 beinga logical 0.

The respiratory motion module 142 is configured to aggregate thedetermined indications of the patient's respiratory motion to provide acomposite signal indicative of the respiratory motion of the patient 22.The module 142 is configured to accumulate, at stage 206, thedifferentiated, or inverted and differentiated signals to form acomposite signal that will indicate the patient's respiratory motion asa function of time. This signal can be plotted to provide a visualindication of the respiration, for example as shown by the trace 220 inFIG. 4.

Referring to FIG. 8, with further reference to FIGS. 1-7, a process 230of detecting respiratory and non-respiratory motion includes the stagesshown. The process 230 is, however, an example only and not limiting.The process 230 can be altered, e.g., by having stages added, removed,rearranged, combined, performed concurrently, and/or having singlestages split into multiple stages.

At stage 232, the process 230 includes transmitting a transmitted signaltoward a subject, the transmitted signal being an ultrasound wave, thetransmitted signal reflecting off the subject to produce a reflectedsignal. The driver 12 produces and provides the drive signal 37 to thetransmitter 14 of the sensor 15. The transmitter 14 transduces the drivesignal 37 into an acoustic ultrasound wave that is transmitted towardthe patient 22 as a transmitted signal. The transmitted signal ispreferably a continuous wave, e.g., with energy being transmitted by thetransmitter 14 nearly uninterrupted (e.g., more than 95% as a functionof time). Further, the transmitted signal preferably has a frequencybetween 30 KHz and 100 KHz, and more preferably between 35 KHz and 45KHz, and more preferably about 40 KHz. A portion of the acousticultrasound signals reflect off the patient 22 as a reflected signal.

At stage 234, the process 230 includes receiving the reflected signaland converting a form of the reflected signal from ultrasound wave toelectrical. The receiver 16 receives the reflected signal and transducesthe reflected signal from an acoustic ultrasound wave to an electricalsignal.

At stage 236, the process 230 includes comparing the reflected signal toat least a first reference signal to determine at least a firstreference phase signal indicative of a first phase difference betweenthe first reference signal and the reflected signal, the at least afirst reference signal being associated with the transmitted signal. Forexample, the comparison module 46 compares the reflected signal 45 withthe reference signal 60 provided by the driver 12, with the reflectedsignal 45 and the reference signal 60 having the same, or nearly thesame, frequency except for, e.g., changes due to the Doppler effect andvariations within the tolerance of the crystal oscillator 32. Thecomparison module 46 produces a signal indicative of the phaserelationship between the reflected signal 45 and the reference signal60. In the example of FIG. 2, the comparison module 46 produces thePhase A signal 92, the polarity bit A signal 94, the Phase B signal 96,and the polarity bit B signal 98 that can be combined to form a signalthat is reliably indicative of the phase relationship of the reflectedsignal 45 to the reference signal 60 over an entire range of phasedifferences. This signal may be unambiguously indicative of this phaserelationship over multiple wavelengths of motion.

At stage 238, the process 230 includes analyzing the first referencephase signal for indicia of respiratory motion of the subject and atleast one of indicia of non-respiratory motion of the subject or indiciaof motion of an entity other than the subject. For example, therespiratory motion module 142 of the signal analyzer 20 analyzes thePhase A signal 92 to determine an indication of respiratory motion ofthe patient 22. The module 142 determines changes in the Phase A signal92 over time to form a signal that represents the respiratory motion ofthe patient 22. For the example implementation of the driver 12 and thephase difference device 18 shown in FIG. 2, the respiratory motionmodule 142 analyzes and combines the Phase A signal 92 over a linearoperation range of the Phase A comparator 54 with the Phase B signal 96during times when the Phase A comparator is outside the desiredoperational range to determine the signal that represents therespiratory motion of the patient 22. Further, the non-respiratorymotion module 140 of the signal analyzer 20 determines the magnitude ofpower in the Phase A signal 92 for different frequency ranges (e.g.,22-50 Hz (and preferably 28-33 Hz) and 0-5 Hz), compares these powermagnitudes, and determines the presence and type of non-respiratorymotion, e.g., by comparing a ratio of the power magnitudes to thresholdsfor different types of non-respiratory motion (motion by the patient 22that is not respiration or non-patient motion).

Referring to FIG. 9, with further reference to FIGS. 1, 2, 6, and 7, amixed analog-and-digital circuit 300 implementation of thenon-respiratory motion module 140 and the respiratory motion module 142shown in FIG. 6 includes the components shown. A section 302 implementsthe non-respiratory motion module 140 and a section 330 implements therespiratory motion module 142. The circuit 300 is configured to performthe example algorithm discussed above with respect to FIG. 7 without useof a computer or microprocessor. The circuit 300 can be realized withstandard high-grade operational amplifiers that are commerciallyavailable, such as the TLE 2081, TLE 2082, or TLE 2084 integratedcircuits made by Texas Instruments Incorporated of Dallas, Tex., USA.These example circuits have very low noise, input offset null, a highslew rate, and more than sufficient output voltage ranges. For some ofthe components, a general purpose operational amplifier is used, such asmodel MC3403 made by Texas Instruments. The components are preferablyoperated with a linear, stabilized +/−9-18 VDC power supply (not shown)and a 5 VDC power supply for the digital circuitry.

In this example, the filter module 152 of the non-respiratory module 140includes a level offset amplifier 304, a band-pass filter (BPF) 306, anda low-pass filter (LPF) 308. The Phase A signal (PA) from the phasedifference device 18 is connected to the level offset amplifier 304 thatoffsets the PA signal, with a range of 0-5V, to +/−2.5V. The leveloffset amplifier 304 may be implemented by a model MC3403 or TLE 208Xseries operational amplifier made by Texas Instruments. The offsetsignal is passed to the BPF 306 and the LPF 308. The BPF 306 ispreferably an 8-pole filter with a center frequency of 30.4 Hz. The LPF308 is preferably an 8-pole filter with a corner frequency of 5 Hz.Examples of the filters 306, 308 can be obtained from FrequencyDevelopment, Inc., Ottawa, Ill., USA, in a variety of implementationswith appropriate transfer characteristics, such as the DP68 seriesfilters. Other analog filtering schemes could be used, e.g., withcontinuous-time active filters such as might be implemented using theMAX 274 8^(th)-order filter by Maxim Integrated, Inc. of Milpitas,Calif., USA, or a switched-capacitor system such as the MAX26X seriesalso by Maxim Integrated, Inc. The filters 306, 308 could also beimplemented by digital signal processing systems in a number ofconfigurations that could also be used to detect a range ofnon-respiratory movement that could be used for separate digitalindications of non-respiratory movement of the subject and anotherentity such as a caretaker.

The power calculating and smoothing module 154 is implemented in thisexample by active rectifiers 310, 312, and a multi-stage log/logoperational amplifier 314. The filtered signals from the filters 306,308 are actively rectified by the rectifiers 310, 312, respectively, andpassed to the multi-stage log/log amplifier 314. Each of the rectifiers310, 312 may be implemented by a model MC3403 or TLE 208X seriesoperational amplifier made by Texas Instruments. The multi-stage log/logamplifier 314 determines the log of the rectified output of the BPF 306and the log of the rectified output of the LPF 308 and provides theresult of each of these logarithms, which is the log of the power ineach of the respective signals, to a difference amplifier 316. Themulti-stage log/log amplifier 314 may be implemented by the duallogarithmic amplifier TL441ICN made by Texas Instruments. Thisintegrated circuit has excellent linearity over a range of 30 dB whichis sufficient to separate the two types of motion.

The comparison module 156 is implemented by the difference amplifier316. The difference amplifier 316 is configured to determine adifference between the logarithm of the rectified output of the BPF 306and the logarithm of the rectified output of the LPF 308. The differencebetween the logarithm of the rectified output of the BPF 306 and thelogarithm of the rectified output of the LPF 308 is equivalent to thelogarithm of the ratio of the power in these signals (i.e., the ratio ofthe power in the corresponding frequency ranges). This logarithmicdifference is similar to the logarithm of the dimensionless numberdiscussed above with respect to FIG. 7. The difference amplifier 316 maybe implemented by a model MC3403 or TLE 208X series operationalamplifier made by Texas Instruments.

The motion type module 158 is implemented in this example by comparators318, 320. The comparators 318, 320 are connected to receive the outputof the difference amplifier 316 and to determine motion of an entityother than the patient 22 (FIG. 1) and non-respiratory motion of thepatient 22, respectively. The comparator 320 is configured to comparethe output of the difference amplifier 316 to one or more appropriatethresholds for non-respiratory motion of the patient 22 and thecomparator 318 is configured to compare the output of the differenceamplifier 316 to an appropriate threshold, e.g., the upper thresholdused by the comparator 320, to indicate whether motion of another entityis present. The thresholds used for the comparisons, and thus theseparate indications of non-respiratory movement of the subject and ofmotion of another entity can be determined by scaling the outputs to thesoftware-derived outputs, discussed with respect to FIG. 7, forequivalency. The output of each of the comparators 318, 320 is a digitalindication of whether the respective type of movement is present. Eitherof the outputs of the comparators 318, 320 could be amplified and usedto drive an LED indicator or other type of display or alarm. The outputof the comparator 320 could be used to gate the respiratory output as anerror condition, that is, respiratory motion may be ignored duringperiods of detected non-respiratory motion. The comparators 318, 320 maybe implemented by the dual differential comparator model LM393 made byTexas Instruments.

The respiratory module 140 is implemented by the components shown in thesection 330. The Phase A (PA) signal 92 (FIG. 2) is provided tocomparators 332, 334 that are configured to detect if the Phase A signalis within the usable range of 0.5 to 4.5V of the comparators 54, 56(FIG. 2). Voltages for comparison may be generated by a resistivenetwork (not shown) connected between a positive digital power supplyand ground. Both of the comparators 332, 334 are configured withhysteresis (e.g., a Schmitt trigger configuration) of approximately0.05V, to reduce noise. The comparator 332 is configured to provide ahigh logic level output if the Phase A signal exceeds 4.5V, and thecomparator 334 is configured to provide a high logic level output if thePhase A signal exceeds 0.5V. Thus, when the Phase A signal is in theusable range of 0.5 to 4.5V, the comparator 332 is at low logic leveland the comparator 334 is at high logic level. The outputs of thecomparators 332, 334 are connected to respective inputs of anexclusive-OR (XOR) gate 336. The XOR gate 336 is configured such thatthe output of the XOR gate 336 will be a high logic level if the outputof the comparator 332 is at a low logic level and the output of thecomparator 334 is at a high logic level, indicating that the Phase Asignal is to be used for indicating/determining respiratory motion ofthe subject 22. If the Phase A signal is out of range, then the outputof the XOR gate 336 is at a low logic level, indicating that the Phase Bsignal is to be used for indicating/determining respiratory motion ofthe subject 22. The output of the XOR gate 336 output is connected to asingle-pole, double-throw (SPDT) analog switch 342 that is configured toselect either a differentiated Phase A signal, when the output of theXOR gate 336 is at a high logic level, or a differentiated Phase Bsignal, when the output of the XOR gate 336 is at a low logic level. Theoutput of the XOR gate 336 is also connected to an SPDT analog switch344 that is configured to select either the polarity bit A (PbA) signal,when the output of the XOR gate 336 is at a high logic level, or thepolarity bit B (PbB) signal, when the output of the XOR gate 336 is at alow logic level.

The PA and PB signals are conditioned by differentiator circuits 338,340 that are configured to produce derivatives of the PA and PB signals,i.e., a differentiated PA signal (dPA) and a differentiated PB signal(dPB), respectively. The circuits 338, 340 are implemented by RCcircuits and operational amplifiers each of whose gains are controlledby an input capacitor and combined input and feedback resistances, andhave capacitive high-frequency blocking in a feedback loop. The gain andfeedback values of each circuit are preferably trimmed so that thederivatives of the PA and PB signals are equal, as well as an inputoffset null so that when the derivatives of the PA and PB signals arezero, then the output of each of the differentiators 348, 350 is zero.The output of the switch 344, either PbA or the PbB, is connected to aninput of a single-pole, double-throw switch 346, whose outputs areconnected to inputs of an amplifier 348. The outputs of the switch 346are connected to and control the amplifier 348 to either follow orinvert an input of the amplifier 348, from the switch 342, according tothe corresponding PbA or PbB. That is, the switch 346 is configured tooutput a “follow” signal if the polarity bit received from the switch344 is a high logic level and to output an “invert” signal if thepolarity bit received from the switch 344 is a low logic level. Theamplifier 348, which may be implemented by a single operationalamplifier, is configured to pass the differentiated signal received fromthe switch 342 while the amplifier 348 receives the “follow” signal fromthe switch 346 and to invert the differentiated signal from the switch342 while the amplifier 348 receives the “invert” signal from the switch346. Thus, an output 350 of the amplifier 348 is the differentiatedPhase A signal (dPA) or the differentiated Phase B signal (dPB)corrected for sign by the PbA signal or the PbB signal. That is, theoutput 350 is the dPA signal while the PA signal is in the range of 0.5to 4.5V and the PbA is a high logic level, is the dPA signal invertedwhile the PA signal is in the range of 0.5 to 4.5V and the PbA is a lowlogic level, is the differentiated Phase B signal (dPB) while the PAsignal is outside the range of 0.5 to 4.5V and the PbB is a high logiclevel, and is the dPB signal inverted while the PA signal is outside therange of 0.5 to 4.5V and the PbB is a low logic level. The output 350 isconnected to a clipping amplifier 352 that is configured to reducehigh-frequency noise due to switching or non-respiratory movement. Anoutput of the clipping amplifier 352 is connected to an integrator 354that is configured to integrate the output of the clipping amplifier 352to produce the respiratory output. The integrator 354 is configured touse a resistive element to return the integrated signal to baseline ifthere is a large output swing with non-respiratory movement.

Components of the section 330 may be implemented by the followingexample components. The comparators 332, 334 may be implemented by thecomparator model LM393 noted above. An example of the XOR gate 336 isthe XOR gate model SN74LVC1G286DBVR made by Texas Instruments. Each ofthe differentiator circuits 338, 340 may be implemented by a TLE 2081operational amplifier made by Texas Instruments. An example of each ofthe switches 342, 344 is a single unit of the quad SPDT analog switchmodel DG333 made by Vishay® Intertechnology, Inc. of Malvern, Pa., USA.The switch 346 may be implemented with another unit of the quad DG333integrated circuit. The operational amplifier 348 in this implementationhas the properties of the TLE2082 integrated circuit made by TexasInstruments. The clipping amplifier 352 and the integrator 354 may eachhave the properties of the TLE2081 integrated circuit made by TexasInstruments.

Experimental Results

Referring to FIG. 10, with further reference to FIG. 1, experimentalresults of an example implementation of the system 10 are shown. Thesubject 22 in this example was an infant weighing approximately twopounds. The signal analyzer 20 was implemented with the algorithm shownin FIG. 7. For simplicity and clarity, the Phase B signal and thePolarity bit B signal are not shown in FIG. 10. The plots in FIG. 10show that the system 10 was able to provide indications of respiratorymovement of the subject 22 (Respiratory Output), non-respiratorymovement of the subject 22 (Infant Movement), and movement of an entityother than the subject 22 (Caretaker Movement). Further, a respirationrate was able to be determined (Resp. Rate Sensor (breaths/m).

Other Considerations

Other examples and implementations are within the scope and spirit ofthe disclosure and appended claims. For example, due to the nature ofsoftware, functions described above can be implemented using softwareexecuted by a processor, hardware, firmware, hardwiring, or combinationsof any of these. Features implementing functions may also be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations.Also, “motion” and “movement” are used herein interchangeably. Also, asused herein, “or” as used in a list of items prefaced by “at least oneof” indicates a disjunctive list such that, for example, a list of “atleast one of A, B, or C” means A or B or C or AB or AC or BC or ABC(i.e., A and B and C), or combinations with more than one feature (e.g.,AA, AAB, ABBC, etc.).

While the discussion above described determining non-respiratory motionby comparing power in a non-respiratory motion frequency band with powerin a respiratory motion frequency band, other techniques may be used todetermine non-respiratory motion. For example, non-respiratory motioncould be determined by analyzing power in the non-respiratory frequencyband alone. For example, the amplitude of a band-pass-filtered signalfor the non-respiratory frequency band could be compared against athreshold power value, with power values in the filtered signal beingabove the threshold indicating that non-respiratory motion is present.Thus, for example, stages 162, 164, 166, 176, 182 of FIG. 7 may beeliminated, and stage 184 modified to be a comparison of the powercalculation of stage 174 against the threshold.

A statement that a value exceeds (or is more than or above) a firstthreshold value is equivalent to a statement that the value meets orexceeds a second threshold value that is slightly greater than the firstthreshold value, e.g., the second threshold value being one value higherthan the first threshold value in the resolution of a computing systemor the capability of analog comparators. A statement that a value isless than (or is within or below) a first threshold value is equivalentto a statement that the value is less than or equal to a secondthreshold value that is slightly lower than the first threshold value,e.g., the second threshold value being one value lower than the firstthreshold value in the resolution of a computing system.

As used herein, unless otherwise stated, a statement that a function oroperation is “based on” an item or condition means that the function oroperation is based on the stated item or condition and may be based onone or more items and/or conditions in addition to the stated item orcondition.

Further, an indication that information is sent or transmitted, or astatement of sending or transmitting information, “to” an entity doesnot require completion of the communication. Such indications orstatements include that the information is conveyed from a sendingentity but does not reach an intended recipient of the information. Theintended recipient, even though not actually receiving the information,may still be referred to as a receiving entity, e.g., a receivingexecution environment.

Substantial variations may be made in accordance with specificrequirements. For example, customized hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

The terms “machine-readable medium” and “computer-readable medium,” asused herein, refer to any medium that participates in providing datathat causes a machine to operate in a specific fashion. Using a computersystem, various computer-readable media might be involved in providinginstructions/code to processor(s) for execution and/or might be used tostore and/or carry such instructions/code (e.g., as signals). In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, includingbut not limited to, non-volatile media and volatile media. Non-volatilemedia include, for example, optical and/or magnetic disks. Volatilemedia include, without limitation, dynamic memory.

Common forms of physical and/or tangible computer-readable mediainclude, for example, a floppy disk, a flexible disk, hard disk,magnetic tape, or any other magnetic medium, a CD-ROM, any other opticalmedium, punchcards, papertape, any other physical medium with patternsof holes, a RAM, a PROM, EPROM, a FLASH-EPROM, any other memory chip orcartridge, a carrier wave as described hereinafter, or any other mediumfrom which a computer can read instructions and/or code.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to one or more processorsfor execution. Merely by way of example, the instructions may initiallybe carried on a magnetic disk and/or optical disc of a remote computer.A remote computer might load the instructions into its dynamic memoryand send the instructions as signals over a transmission medium to bereceived and/or executed by a computer system.

The methods, systems, and devices discussed above are examples. Variousconfigurations may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods may be performed in an order different from that described,and that various steps may be added, omitted, or combined. Also,features described with respect to certain configurations may becombined in various other configurations. Different aspects and elementsof the configurations may be combined in a similar manner. Also,technology evolves and, thus, many of the elements are examples and donot limit the scope of the disclosure or claims.

Specific details are given in the description to provide a thoroughunderstanding of example configurations (including implementations).However, configurations may be practiced without these specific details.For example, well-known circuits, processes, algorithms, structures, andtechniques have been shown without unnecessary detail in order to avoidobscuring the configurations. This description provides exampleconfigurations only, and does not limit the scope, applicability, orconfigurations of the claims. Rather, the preceding description of theconfigurations provides a description for implementing describedtechniques. Various changes may be made in the function and arrangementof elements without departing from the spirit or scope of thedisclosure.

Also, configurations may be described as a process which is depicted asa flow diagram or block diagram. Although each may describe theoperations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be rearranged. A process may have additional stages orfunctions not included in the figure. Furthermore, examples of themethods may be implemented by hardware, software, firmware, middleware,microcode, hardware description languages, or any combination thereof.When implemented in software, firmware, middleware, or microcode, theprogram code or code segments to perform the tasks may be stored in anon-transitory computer-readable medium such as a storage medium.Processors may perform the described tasks.

Components, functional or otherwise, shown in the figures and/ordiscussed herein as being connected or coupled or communicativelycoupled or as communicating with each other are communicatively coupled.That is, they may be directly or indirectly connected to enablecommunication between them.

Having described several example configurations, various modifications,alternative constructions, and equivalents may be used without departingfrom the spirit of the disclosure. For example, the above elements maybe components of a larger system, wherein other rules may takeprecedence over or otherwise modify the application of the invention.Also, a number of operations may be undertaken before, during, or afterthe above elements are considered. Accordingly, the above descriptiondoes not bound the scope of the claims.

Further, more than one invention may be disclosed.

The invention claimed is:
 1. A method of detecting motion, the methodcomprising: transmitting a transmitted signal toward a subject, thetransmitted signal being an ultrasound wave, the transmitted signalreflecting off the subject to produce a reflected signal; receiving thereflected signal and converting a form of the reflected signal fromultrasound wave to electrical; comparing, by a first phase comparator,the reflected signal to a first reference signal to determine a firstreference phase signal indicative of a first phase difference betweenthe first reference signal and the reflected signal, the first referencesignal being associated with the transmitted signal; comparing, by asecond phase comparator, the reflected signal to a second referencesignal to determine a second reference phase signal indicative of asecond phase difference between the second reference signal and thereflected signal, the second reference signal being out of phase withrespect to the first reference signal; using the first reference phasesignal only, from among the first reference phase signal and the secondreference phase signal, when the second reference phase signal is in anout-of-specification zone of the second phase comparator, to determinerespiratory motion of the subject; and using the second reference phasesignal only, from among the first reference phase signal and the secondreference phase signal, when the first reference phase signal is in anout-of-specification zone of the first phase comparator, to determinethe respiratory motion of the subject.
 2. The method of claim 1, furthercomprising using the first reference phase signal to determinenon-respiratory motion by: filtering the first reference phase signalinto a first portion within a first frequency range and a second portionwithin a second frequency range, the second frequency range beingseparate from the first frequency range; and analyzing a combination ofthe first portion of the first reference phase signal and the secondportion of the first reference phase signal for the non-respiratorymotion; wherein the non-respiratory motion includes at least one ofnon-respiratory motion of the subject or motion of an entity other thanthe subject.
 3. The method of claim 2, wherein the analyzing thecombination comprises determining a dimensionless magnitude associatedwith the combination.
 4. The method of claim 3, further comprising:determining that the non-respiratory motion of the subject is occurringin response to the dimensionless magnitude being above a first thresholdand below a second threshold; and determining that the motion of theentity is occurring in response to the dimensionless magnitude beingabove the second threshold.
 5. The method of claim 3, wherein thedetermining the dimensionless magnitude comprises dividing a power valueof the second portion of the first reference phase signal by a powervalue of the first portion of the first reference phase signal.
 6. Themethod of claim 5, wherein the first portion of the first referencephase signal is within a frequency range between 0 Hz and 5 Hz, and thesecond portion of the first reference phase signal is within a frequencyrange between 22 Hz and 50 Hz.
 7. The method of claim 2, wherein thefirst frequency range is associated with the respiratory motion of thesubject and the second frequency range is associated with thenon-respiratory motion.
 8. The method of claim 1, wherein: the firstreference signal and the transmitted signal are both derived from acommon electrical drive signal; the using the first reference phasesignal to determine the respiratory motion of the subject yields firstindicia of the respiratory motion of the subject; the using the secondreference phase signal to determine the respiratory motion of thesubject yields second indicia of the respiratory motion of the subject;and the method further comprises: forming composite indicia of therespiratory motion of the subject comprising the second indicia of therespiratory motion of the subject corresponding to when the firstreference phase signal is in the out-of-specification zone of the firstphase comparator, and comprising the first indicia of the respiratorymotion of the subject otherwise.
 9. The method of claim 1, wherein thetransmitting comprises transmitting a continuous wave ultrasound signal,having a fixed frequency between 30 KHz and 100 KHz, as the transmittedsignal.
 10. The method of claim 1, further comprising analyzing thefirst reference phase signal for non-respiratory motion by comparing apower level in a non-respiratory frequency range portion of the firstreference phase signal with a threshold power level.
 11. The method ofclaim 1, wherein the transmitted signal is of a transmit frequency,wherein the first reference signal is of the transmit frequency, andwherein the second reference signal is of the transmit frequency and is90° out of phase with respect to the first reference signal.
 12. Amotion-detection system comprising: a driver configured to produce adrive signal and to produce, from the drive signal, a transmittersignal, a first reference signal, and a second reference signal: anultrasound transmitter communicatively coupled to the driver andconfigured to transmit a transmitted signal toward a subject in responseto the transmitter signal, the transmitted signal being an ultrasoundwave; a receiver configured to receive a reflected signal and convert aform of the reflected signal from ultrasound wave to electrical; a phasedifference device, including a first phase comparator and a second phasecomparator, communicatively coupled to the driver and the receiver,configured to: compare the reflected signal to the first referencesignal to determine a first reference phase signal indicative of a firstphase difference between the first reference signal and the reflectedsignal, the first reference signal being associated with the drivesignal; and compare the reflected signal to the second reference signalto determine a second reference phase signal indicative of a secondphase difference between the second reference signal and the reflectedsignal, the second reference signal being out of phase with respect tothe first reference signal; and a signal analyzer communicativelycoupled to the phase difference device and configured to: use the firstreference phase signal only, from among the first reference phase signaland the second reference phase signal, when the second reference phasesignal is in an out-of-specification zone of the second phasecomparator, to determine respiratory motion of the subject; and use thesecond reference phase signal only, from among the first reference phasesignal and the second reference phase signal, when the first referencephase signal is in an out-of-specification zone of the first phasecomparator, to determine the respiratory motion of the subject.
 13. Thesystem of claim 12, wherein the signal analyzer is further configuredto: filter the first reference phase signal into a first frequencyportion within a first frequency range and a second frequency portionwithin a second frequency range, the second frequency range beingseparate from the first frequency range; and analyze a combination ofthe first frequency portion of the first reference phase signal and thesecond frequency portion of the first reference phase signal todetermine non-respiratory motion, the non-respiratory motion includingat least one of non-respiratory motion of the subject or motion of anentity other than the subject.
 14. The system of claim 13, wherein todetermine the non-respiratory motion the signal analyzer is configuredto: determine a dimensionless magnitude associated with the combinationof the first frequency portion of the first reference signal and thesecond frequency portion of the first reference phase signal; provide anindication that the non-respiratory motion of the subject is occurringif the dimensionless magnitude is above a first threshold and below asecond threshold; and provide an indication that the motion of theentity is occurring if the dimensionless magnitude is above the secondthreshold.
 15. The system of claim 14, wherein the signal analyzer isconfigured to determine the dimensionless magnitude by dividing a powervalue of the second frequency portion of the first reference phasesignal by a power value of the first frequency portion of the firstreference phase signal.
 16. The system of claim 15, wherein the firstfrequency portion of the first reference phase signal is within afrequency range between 0 Hz and 5 Hz, and the second frequency portionof the first reference phase signal is within a frequency range between22 Hz and 50 Hz.
 17. The system of claim 13, wherein the first frequencyrange is associated with the respiratory motion of the subject and thesecond frequency range is associated with the non-respiratory motion.18. The system of claim 12, wherein: the second reference signal is aphase-shifted version of the first reference signal; and the signalanalyzer is configured to form a composite subject respiratory signal bycombining a first phase-differential portion of the first referencephase signal with a second phase-differential portion of the secondreference phase signal, the first phase-differential portion of thefirst reference phase signal in the composite subject respiratory signalcorresponding to a first linear range of the first phase comparator andthe second phase-differential portion of the second reference phasesignal in the composite subject respiratory signal corresponding to asecond linear range of the second phase comparator, the signal analyzerbeing to form the composite subject respiratory signal with the secondphase-differential portion and without the first phase-differentialportion corresponding to when the first phase-differential portion ofthe first reference phase signal is outside the first linear range. 19.The system of claim 12, wherein the driver is configured to produce thetransmitter signal with a frequency between 35 KHz and 45 KHz.
 20. Thesystem of claim 12, wherein the signal analyzer is configured to comparea power level in a non-respiratory frequency range portion of the firstreference phase signal with a threshold power level.